What is Acromion?

Acromion is the extension of the spine of the scapula. Acromion articulates with the clavicle or the collarbone of the pectoral girdle by the acromioclavicular joint.

Acromion

The acromion is a part of the scapula bone or shoulder blade of the pectoral girdle. It is a bony process.

There is an elevated ridge present on the dorsal surface of the scapula bone, which is known as the spine. The spine divides the dorsal surface of the scapula into two unequal parts. The spine projects out laterally as a flat process known as the acromion, which is curved upwards.

The acromion of the scapula (acron = summit;omos = shoulder) is a flattened piece of bone that lies subcutaneously forming the top of the shoulder. The posterior end of its lateral border is called the acromial angle, where it is continuous with the scapula. The anterior end of its medial border articulates with the clavicle at the acromioclavicular joint.

Acromion Structure

The acromion has two borders, medial and lateral; two surfaces, superior and inferior; and a facet for the clavicle

Acromion surfaces – Its superior surface is convex and rough while its inferior surface is concave and smooth. The lateral border presents three or four tubercles for the origin of the deltoid. The medial gives attachment to the trapezius and articulates with the clavicle. 

Acromion borders – Its lateral border is irregular and thick. The medial border is comparatively shorter and is concave. 

Any type of shoulder injuries, osteoarthritis, rotator cuff tears can lead to acromion pain.

Acromion Types

Acromion bone can be morphologically classified (Bigliani classification) into three types –

1. Type Ⅰ – Flat Acromion 
2. Type Ⅱ – Hooked Acromion 
3. Type Ⅲ – Curved Acromion 

Flat is the most inferior type among the three and curved is the most common acromion bone shape. Also, some recent classifications include a fourth type which comprises upturned or convex acromion.

Acromioclavicular Joint

The junction between the acromion and the clavicle is called the acromioclavicular joint. It is a plane synovial joint present at the top of the shoulder. 

The clavicle lies horizontally at the root of the neck, separating it from the front of the chest. The bone is subcutaneous, and therefore, palpable, throughout its length. Medially, it articulates with the sternum at the sternoclavicular joint, and laterally with the acromion at the acromioclavicular joint. Both the joints are palpable because of the upward projecting ends of the clavicle. 

The acromial end of the clavicle and the acromion are connected by the acromioclavicular ligaments. The ligament covering the superior part of articulation is called the superior acromioclavicular ligament and the under part is called the inferior acromioclavicular ligament.

This was in brief about the Acromion. Get access to all the NEET Questions with explanations, only at BYJU’S.

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